English oak acornAcorns of the willow oak in South Carolina (from small to large, counterclockwise from center): Q.phellos (willow oak), Q.falcata (southern red oak; top right), Q.alba (white oak), and Q.coccinea (scarlet oak). Scale bar at upper right is 1cm.Diagram of the anatomy of an acorn: A.) Cupule B.) Pericarp (fruit wall) C.) Seed coat (testa) D.) Cotyledons (2) E.) Plumule F.) Radicle G.) Remains of style. Together D., E., and F. make up the embryo.
The acorn is the nut of the oaks and their close relatives (genera Quercus, Notholithocarpus and Lithocarpus, in the family Fagaceae). It usually contains a seedling surrounded by two cotyledons (seedling leaves), enclosed in a tough shell known as the pericarp, and borne in a cup-shaped cupule.[1][2] Acorns are 1–6cm (1⁄2–2+1⁄2in) long and 0.8–4cm (3⁄8–1+5⁄8in) on the fat side. Acorns take between 5 and 24 months (depending on the species) to mature; see the list of Quercus species for details of oak classification, in which acorn morphology and phenology are important factors.
The word acorn (earlier akerne, and acharn) is related to the Gothic name akran, which had the sense of "fruit of the unenclosed land".[3] The word was applied to the most important forest produce, that of the oak. Chaucer spoke of "achornes of okes" in the 14th century. By degrees, popular etymology connected the word both with "corn" and "oak-horn", and the spelling changed accordingly.[4] The current spelling (emerged c.15th–16th century) derives from association with ac (Old English: "oak") + corn.[5]
Ecology
Ponies eating acorns. Acorns can cause painful death in equines, especially if eaten in excess.Sprouting acorn of Quercus robur
Acorns play an important role in forest ecology when oaks are plentiful or dominant in the landscape.[6] The volume of the acorn crop may vary widely, creating great abundance or great stress on the many animals dependent on acorns and the predators of those animals.[7] Acorns, along with other nuts, are termed mast.
Wildlife that consume acorns as an important part of their diets include birds, such as jays, pigeons, some ducks, and several species of woodpeckers. Small mammals that feed on acorns include mice, squirrels and several other rodents. One beetle species, Thorectes lusitanicus, also feeds on acorns.[8] Acorns have a large influence on small rodents in their habitats, as large acorn yields help rodent populations to grow.[9]
Large mammals such as pigs, bears, and deer also consume large amounts of acorns; they may constitute up to 25% of the diet of deer in the autumn.[10] In Spain, Portugal and the New Forest region of southern England, pigs are still turned loose in dehesas (large oak groves) in the autumn, to fill and fatten themselves on acorns. Heavy consumption of acorns can, on the other hand, be toxic to other animals that cannot detoxify their tannins, such as horses and cattle,[11][12] especially if eaten in excess.[13][14][15]
The larvae of some moths and weevils also live in young acorns, consuming the kernels as they develop.[16]
Acorns are attractive to animals because they are large and thus efficiently consumed or cached. Acorns are also rich in nutrients. Percentages vary from species to species, but all acorns contain large amounts of protein, carbohydrates and fats, as well as the minerals calcium, phosphorus and potassium, and the vitaminniacin. Total food energy in an acorn also varies by species, but all compare well with other wild foods and with other nuts.[17]
Acorns also contain bitter tannins, the amount varying with the species. Since tannins, which are plant polyphenols, interfere with an animal's ability to metabolize protein, creatures must adapt in different ways to use the nutritional value acorns contain. Animals may preferentially select acorns that contain fewer tannins. When the tannins are metabolized in cattle, the tannic acid produced can cause ulceration and kidney failure.[12]
Animals that cache acorns, such as jays and squirrels, may wait to consume some of these acorns until sufficient groundwater has percolated through them to leach out the tannins. Other animals buffer their acorn diet with other foods. Many insects, birds, and mammals metabolize tannins with fewer ill effects than do humans.
Species of acorn that contain large amounts of tannins are very bitter, astringent, and potentially irritating if eaten raw. This is particularly true of the acorns of American red oaks and English oaks. The acorns of white oaks, being much lower in tannins, are nutty in flavor; this characteristic is enhanced if the acorns are given a light roast before grinding.
Tannins can be removed by soaking chopped acorns in several changes of water, until the water no longer turns brown. Cold water leaching can take several days, but three to four changes of boiling water can leach the tannins in under an hour.[18] Hot water leaching (boiling) cooks the starch of the acorn, which would otherwise act like gluten in flour, helping it bind to itself. For this reason, if the acorns will be used to make flour, then cold water leaching is preferred.[19]
Being rich in fat, acorn flour can spoil or molder easily and must be carefully stored. Acorns are also sometimes prepared as a massage oil.
Acorns of the white oak group, Leucobalanus, typically start rooting as soon as they are in contact with the soil (in the fall), then send up the leaf shoot in the spring.
Dispersal agents
Acorns are too heavy for wind dispersal, so they require other ways to spread. Oaks therefore depend on biological seed dispersal agents to move the acorns beyond the mother tree and into a suitable area for germination (including access to adequate water, sunlight and soil nutrients), ideally a minimum of 20–30m (70–100ft) from the parent tree[citation needed].
Many animals eat unripe acorns on the tree or ripe acorns from the ground, with no reproductive benefit to the oak, but some animals, such as squirrels and jays serve as seed dispersal agents. Jays and squirrels that scatter-hoard acorns in caches for future use effectively plant acorns in a variety of locations in which it is possible for them to germinate and thrive.
Even though jays and squirrels retain remarkably large mental maps of cache locations and return to consume them, the odd acorn may be lost, or a jay or squirrel may die before consuming all of its stores. A small number of acorns manage to germinate and survive, producing the next generation of oaks.
Scatter-hoarding behavior depends on jays and squirrels associating with plants that provide good packets of food that are nutritionally valuable, but not too big for the dispersal agent to handle. The beak sizes of jays determine how large acorns may get before jays ignore them.
Acorns germinate on different schedules, depending on their place in the oak family. Once acorns sprout, they are less nutritious, as the seed tissue converts to the indigestible lignins that form the root.[20]
In some cultures, acorns once constituted a dietary staple, though they have largely been replaced by grains and are now typically considered a relatively unimportant food, except in some Native American and Korean communities.
Several cultures have devised traditional acorn-leaching methods, sometimes involving specialized tools, that were traditionally passed on to their children by word of mouth.[23][24]
Acorns served an important role in early human history and were a source of food for many cultures around the world.[25] For instance, the Ancient Greek lower classes and the Japanese (during the Jōmon period)[26] would eat acorns, especially in times of famine.[citation needed] In ancient Iberia they were a staple food, according to Strabo. Despite this history, acorns rarely form a large part of modern diets and are not currently cultivated on scales approaching that of many other nuts. However, if properly prepared (by selecting high-quality specimens and leaching out the bitter tannins in water), acorn meal can be used in some recipes calling for grain flours. In antiquity, Pliny the Elder noted that acorn flour could be used to make bread.[27] Varieties of oak differ in the amount of tannin in their acorns. Varieties preferred by Native Americans, such as Quercus kelloggii (California black oak), may be easier to prepare or more palatable.[28]
In Korea, an edible jelly named dotorimuk is made from acorns, and dotori guksu are Korean noodles made from acorn flour or starch. In the 17th century, a juice extracted from acorns was administered to habitual drunkards to cure them of their condition or else to give them the strength to resist another bout of drinking.[citation needed][clarification needed]
Roasted acorn flour is a main ingredient in sweet cakes special to Kurdish areas of Iran and Iraq.[29][30]
Acorns have frequently been used as a coffee substitute, particularly when coffee was unavailable or rationed. The Confederates in the American Civil War and Germans during World War I (when it was called Ersatz coffee), which were cut off from coffee supplies by Union and Allied blockades respectively, are particularly notable past instances of this use of acorns.
Use by Native Americans
Acorns are a traditional food of many indigenous peoples of North America, and long served an especially important role for Californian Native Americans, where the ranges of several species of oaks overlap, increasing the reliability of the resource.[31] One ecology researcher of Yurok and Karuk heritage reports that "his traditional acorn preparation is a simple soup, cooked with hot stones directly in a basket," and says he enjoys acorns eaten with "grilled salmon, huckleberries or seaweed."[32] Unlike many other plant foods, acorns do not need to be eaten or processed right away, but may be stored for a long time, much as squirrels do. In years that oaks produced many acorns, Native Americans sometimes collected enough acorns to store for two years as insurance against poor acorn production years.
After drying in the sun to discourage mould and germination, acorns could be cached in hollow trees or structures on poles to keep them safe from mice and squirrels. Stored acorns could then be used when needed, particularly during the winter when other resources were scarce. Acorns that germinated in the fall were shelled and pulverized before those germinating in spring. [citation needed] Because of their high fat content, stored acorns can become rancid. Moulds may also grow on them.
The lighting of ground fires killed the larvae of acorn moths and acorn weevils by burning them during their dormancy period in the soil. The pests can infest and consume more than 95% of an oak's acorns. [citation needed]
Fires also released the nutrients bound in dead leaves and other plant debris into the soil, thus fertilizing oak trees while clearing the ground to make acorn collection easier. Most North American oaks tolerate light fires, especially when consistent burning has eliminated woody fuel accumulation around their trunks. Consistent burning encouraged oak growth at the expense of other trees less tolerant of fire, thus keeping oaks dominant in the landscapes. [citation needed]
Oaks produce more acorns when they are not too close to other oaks and thus competing with them for sunlight, water and soil nutrients. The fires tended to eliminate the more vulnerable young oaks and leave old oaks which created open oak savannas with trees ideally spaced to maximize acorn production.
An oak is a hardwood tree or shrub in the genus Quercus of the beech family. They have spirally arranged leaves, often with lobed edges, and a nut called an acorn, borne within a cup. The genus is widely distributed in the Northern Hemisphere; it includes some 500 species, both deciduous and evergreen. Fossil oaks date back to the Middle Eocene. Molecular phylogeny shows that the genus is divided into Old World and New World clades, but many oak species hybridise freely, making the genus's history difficult to resolve.
Quercus kelloggii, the California black oak or Kellogg oak, is an oak in the red oak section native to western North America. Although genetically separated from them for more than 20 million years, its leaves are remarkably similar in appearance to several other members of the red oak section including the red oak and the black oak found in eastern and central North America.
Tannins are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids.
Quercus rubra, the northern red oak, is an oak tree in the red oak group. It is a native of North America, in the eastern and central United States and southeast and south-central Canada. It has been introduced to small areas in Western Europe, where it can frequently be seen cultivated in gardens and parks. It prefers good soil that is slightly acidic. Often simply called red oak, northern red oak is so named to distinguish it from southern red oak (Q. falcata), also known as the Spanish oak. Northern red oak is sometimes called champion oak.
Quercus alba, the white oak, is one of the preeminent hardwoods of eastern and central North America. It is a long-lived oak, native to eastern and central North America and found from Minnesota, Ontario, Quebec, and southern Maine south as far as northern Florida and eastern Texas. Specimens have been documented to be over 450 years old.
Quercus garryana is an oak tree species of the Pacific Northwest, with a range stretching from southern California to southwestern British Columbia. It is commonly known as the Garry oak, Oregon white oak or Oregon oak. It grows from sea level to an altitude of 690 feet in the northern part of its range, and from 980 to 5,900 ft in the south of the range in California. The eponymous Nicholas Garry was deputy governor of the Hudson's Bay Company.
Corylus cornuta, the beaked hazelnut, is a deciduous shrubby hazel with two subspecies found throughout most of North America.
Hoarding or caching in animal behavior is the storage of food in locations hidden from the sight of both conspecifics and members of other species. Most commonly, the function of hoarding or caching is to store food in times of surplus for times when food is less plentiful. However, there is evidence that a certain amount of caching or hoarding is actually undertaken with the aim of ripening the food so stored, and this practice is thus referred to as ‘ripening caching’. The term hoarding is most typically used for rodents, whereas caching is more commonly used in reference to birds, but the behaviors in both animal groups are quite similar.
The fox squirrel, also known as the eastern fox squirrel or Bryant's fox squirrel, is the largest species of tree squirrel native to North America. Despite the differences in size and coloration, it is sometimes mistaken for American red squirrels or eastern gray squirrels in areas where the species co-exist.
Quercus gambelii, with the common name Gambel oak, is a deciduous small tree or large shrub that is widespread in the foothills and lower mountains of western North America. It is also regionally called scrub oak, oak brush, and white oak.
Quercus lobata, commonly called the valley oak or roble, is the largest of the California oaks. It is endemic to the state, growing in interior valleys and foothills from Siskiyou to San Diego counties. Deciduous, it requires year-round groundwater, and may live up to 600 years. Its thick, ridged bark and deeply lobed leaves are characteristic, and assist in identification.
Salinan is the historical indigenous language of the Salinan people of the central coast of California. It has been extinct since the death of the last speaker in 1958.
Quercus chrysolepis, commonly termed canyon live oak, canyon oak, golden cup oak or maul oak, is a North American species of evergreen oak that is found in Mexico and in the western United States, notably in the California Coast Ranges. This tree is often found near creeks and drainage swales growing in moist cool microhabitats. Its leaves are a glossy dark green on the upper surface with prominent spines; a further identification arises from the leaves of canyon live oak being geometrically flat.
Quercus durata, commonly known as leather oak, is a species of oak endemic to California, common in the Coast Ranges and the foothills of the Sierra Nevada. It is found nearly exclusively on serpentine soil and thus is a strong indicator species for this soil type. The common name "leather oak" is derived from the leathery texture on the lop of its leaves. Taxonomically it is placed in the white oak group.
Quercus dumosa is a species of plant in the family Fagaceae, belonging to the white oak section of the oak genus (Quercus). This tree goes by the common names coastal sage scrub oak and Nuttall's scrub oak.
Acorn noodle soup, called dotoriguksu in Korean, is a noodle soup consisting of Korean noodles made from acorn flour or starch, salt, and a combination of grain-based flour.
Quercus ilicifolia, commonly known as bear oak or scrub oak, is a small shrubby oak native to the Eastern United States and, less commonly, in southeastern Canada. Its range in the United States extends from Maine to North Carolina, with reports of a few populations north of the international frontier in Ontario. The name ilicifolia means "holly-leaved."
Quercus pagoda, the cherrybark oak, is one of the most highly valued red oaks in the southern United States. It is larger and better formed than southern red oak and commonly grows on more moist sites. Its strong wood and straight form make it an excellent timber tree. Many wildlife species use its acorns as food, and cherrybark oak makes a fine shade tree. Cherrybark oak was formerly considered to be a subspecies of southern red oak, Quercus falcata, subsp pagodifolia.
Quercus rotundifolia, the holm oak or ballota oak, is an evergreen oak native to the western Mediterranean region, with the majority of the population in the Iberian Peninsula and minor populations in Northwest Africa. The species was first described by Jean-Baptiste Lamarck in 1785. It is the typical species of the Iberian dehesa or montado, where its sweet-astringent acorns are a source of food for livestock, particularly the Iberian pig. Its acorns have also been used for human nourishment since the Neolithic era. It is placed in section Ilex. Some authors described it as a subspecies of Quercus ilex.
Notholithocarpus densiflorus, commonly known as the tanoak or tanbark-oak, is a broadleaf tree in the family Fagaceae, and the type species of the genus Notholithocarpus. It is native to the far western United States, particularly Oregon and California. It ranges from 15–40 meters in height, with a trunk diameter of 60–190 centimeters.
↑ Barrett, Reginald H. (1980). "Mammals of California Oak Habitats-Management Implications"(PDF). In Plumb, Timothy R. (ed.). Proceedings of the symposium on the ecology, management, and utilization of California oaks, June 26–28. USDA Forest Service General Technical Report PSW-044. pp.276–291.
1 2 Barringer, Sam. "Acorns Can be Deadly". West Virginia University Extension Service. Archived from the original on 27 February 2014. Retrieved 27 January 2014.
↑ Brown, Leland R. (1979) Insects Feeding on California Oak Treesin Proceedings of the Symposium on Multiple-Use Management of California's Hardwood Resources, Timothy Plum and Norman Pillsbury (eds.).
↑ Janzen, Daniel H. (1971), Richard F. Johnson, Peter W. Frank and Charles Michner (ed.), "Seed Predation by Animals", Annual Review of Ecology and Systematics, 2: 465–492, doi:10.1146/annurev.es.02.110171.002341, JSTOR2096937
↑ National Academies of Sciences, Engineering, and Medicine; Health and Medicine Division; Food and Nutrition Board; Committee to Review the Dietary Reference Intakes for Sodium and Potassium (2019). Oria, Maria; Harrison, Meghan; Stallings, Virginia A. (eds.). Dietary Reference Intakes for Sodium and Potassium. The National Academies Collection: Reports funded by National Institutes of Health. Washington, DC: National Academies Press (US). ISBN978-0-309-48834-1. PMID30844154. Archived from the original on 9 May 2024. Retrieved 21 June 2024.
↑ Alphonso, Christina (5 November 2015). "Acres of Acorns". The Metropolitan Museum of Art, i.e. The Met Museum. Retrieved 15 April 2017.
↑ Derby, Jeanine A. (1980). "Acorns-Food for Modern Man"(PDF). In Plumb, Timothy R. (ed.). Proceedings of the symposium on the ecology, management, and utilization of California oaks, June 26–28. USDA Forest Service General Technical Report PSW-044. pp.360–361.
↑ Salih, Rafiq Mohamed; Sabir, Dlir Amin; Hawramee, Othman K. (October 2013). "Effect of sweet acorn flour of common oak (Quercus aegilops L.) on locally Iraqi pastry (kulicha) products". Journal of Zankoy Sulaimani - Part A. 16 (special): 244–249. doi:10.17656/jzs.10327.
↑ Suttles, Wayne (1964), "(Review of) Ecological Determinants of Aboriginal California Populations, by Martin A. Baumhoff", American Anthropologist, vol.66, no.3, p.676, doi:10.1525/aa.1964.66.3.02a00360
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